IKKg is a component of the IKK complex, which regulates NF-kB activity. To investigate the role of IKKg, we expressed wild type IKKg containing 412 amino acids, and deletion mutants containing residues 1-312 and 101-412, using murine IKKg cDNA. In a co-transfection assay with a CAT reporter plasmid, NIK activated NF-kB-dependent gene expression approximately two fold and this expression was inhibited by co-transfection of a wild type IKKg expression plasmid. In binding assays IKKg inhibited the association of IkBa with IKKb and the subsequent phosphorylation of IkBa that is activated by NIK. Inhibition by IKKg also occurred in an assay with a dominant negative mutant of NIK but not with a C-terminal deletion mutant of IKKg, indicating that the C-terminal 100 amino acids of IKKg are important for negative regulation of NF-kB activation. In addition, the interaction of IKKb with IKKg was inhibited by co-transfection with a NIK expression plasmid. Our results suggest that overexpression of IKKg inhibits activation of NF-kB by NIK by competing with NIK for interaction with IKKb.

Keywords: IkB Kinases, IKK Complex, IKKg, NF-kB Activation, NIK, Signal Transduction